Induction-type rotational position detection devices of the type which produce two-phase outputs (i.e., outputs of sine and cosine phases) in response to a single-phase exciting input are commonly known as “resolvers”, and induction-type rotational position detection devices of the type which produce three-phase outputs (i.e., outputs of three phases shifted from each other by 120°) in response to a single-phase exciting input are commonly known as “synchros”. In the resolvers in the most traditional form, a stator includes two-pole (sine and cosine poles) secondary windings that intersect each other at a 90° mechanical angle, and a rotor includes a primary winding. The resolvers of this type are not satisfactory in that they need a brush to electrically contact the primary winding of the rotor. There have also been known brush-less resolvers that require no such brush; that is, these brush-less resolvers include, in the rotor, a rotary transformer in place of the brush. However, because of the provision of the rotary transformer in the rotor, it is difficult to reduce the overall size of the devices and thus there are limitations to the downsizing of the brush-less resolvers. Further, the provision of the rotary transformer increases the number of the component parts, which also leads to an unavoidable increase in the manufacturing cost.
Also known in the art are rotational position detection devices of the non-contact/variable-reluctance type (known in the past by the trade name “microsyn”), where a stator includes primary and secondary windings disposed on a plurality of projecting poles and a rotor is formed of a magnetic body having a predetermined shape (such as an elliptical circular shape, an oval shape or a shape having a projection). In these rotational position detection devices (rotary-type position detection devices), a reluctance variation responding to a rotational position of the object to be detected is produced on the basis of variations in gaps between the stator's projecting poles and the rotor's magnetic body that occur in response to a changing rotational position of the object to be detected, so that an output signal corresponding to the reluctance variation is provided. Further, similar reluctance-based rotational position detection devices are also disclosed, for example, in Patent Literature 1, 2 and 3. As position detection techniques based on the detector output signal, there have been known both a phase-based scheme in which position detecting data corresponds to an electrical phase angle of the output signal and a voltage-based scheme in which position detecting data corresponds to a voltage level of the output signal. In the case where the phase-based scheme is employed, the individual primary windings disposed at different mechanical angles are excited by phase-shifted inputs, such as two-phase or three-phase exciting inputs, so as to generate a single-phase output signal having a different electrical angle corresponding to a current rotational position. Further, in the case where the voltage-based scheme is employed, the relationship between the primary and secondary windings is reversed from that in the phase-based scheme, and plural-phase outputs are produced in response to a single-phase exciting input in the same manner as in the resolvers.
Typically, the rotational position detection devices, such as the resolvers, which produce plural-phase outputs in response to a single-phase, are arranged to produce two-phase outputs, namely, sine-phase and cosine-phase outputs. To this end, in the conventional resolver-style rotational position detection devices of the non-contact/variable-reluctance type, the stator has at least four poles that are spaced apart from each other by a mechanical angle of 90°; specifically, if the first pole is set to a sine phase, the second pole 90° apart from the first pole is set to a cosine phase, the third pole 90° apart from the second pole is set to a minus sine phase and the fourth pole 90° apart from the third pole is set to a minus cosine phase. In such a case, to bring about a reluctance variation, corresponding to a rotation of the object to be detected, in each of the stator poles, the rotor is formed of a magnetic or electrically-conductive substance into an elliptical circular shape, oval shape or cyclic shape such as a gear shape. Primary and secondary windings are disposed on each of the stator poles so that reluctance in a magnetic circuit passing through the stator pole is changed in response to a variation in a gap between the stator pole and the rotator. The reluctance change causes a degree of magnetic coupling between the primary and secondary coils on each of the stator poles to vary in correspondence with a rotational position of the object to be detected, and thus an output signal corresponding to the rotational position is induced in each of the secondary winding, with the result that a peak amplitude characteristic in the output signal from each of the stator poles presents a cyclic function characteristic.
However, because the known resolver-style rotational position detection devices of non-contact/variable-reluctance type such as discussed above are based on primary-secondary induction by the provision of the primary and secondary coils, a number of coils are required; hence, there is a limit to reduce an overall size of the device as well as a manufacturing cost.
On the other hand, Patent Literatures 4, 5 and 6 disclose impedance measurement type position detection devices constructed to include only a primary coil as sensor coil and to omit a secondary coil. In such case, in the know position detection device, to take out a detection output voltage from the position detection device, a voltage-dividing resistance (fixed resistance) is connected in series with the primary coil, and a detection output voltage is taken out from a connection point (voltage-dividing point) between the resistance and the coil.